Since an internal combustion engine has its torque characteristics and composition of exhaust gas variable with ignition timing, it is lately required to widely adjust the ignition timing in an optimum manner or in association with the opening and closure of a throttle valve to provide characteristics suited to the operating condition of the engine. In an internal combustion engine employed for a motor boat, for example, the ignition timing has been often varied by an angle of approximately 30.degree. to 40.degree. where trolling is desired to be effected or where the deceleration is abruptly effected. One of the prior art ignition systems adapted to widely adjust the ignition timing of the engine is of type having a generator connected by a linkage or any other means to the crank shaft of the engine for rotation therewith. However, such prior art system requires not only substantial force to displace the generator on adjustment of the ignition timing, but also the high precision of a mechanical adjusting mechanism for the linkage. With the system having such mechanical adjusting mechanism, various situations tend to occur in which the ignition timing is shifted and in which the smooth operation is obstructed due to rust on the mechanically engaging portions of the linkage or to foreign matter deposited thereon.